Page History: Perimeter Alerts

Page Revision: 02/09/2009 3:53 PM

Automatically detect approaching weather threats

Perimeter Alerts are one of the most powerful features in Weather Defender, providing you with the capability to automatically detect weather threats and be alerted via screen, email, or mobile device in time to take necessary action.

1 - How it Works

Whenever a weather or dynamic layer is updated, Weather Defender performs a scan of all Alert Perimeters monitoring that layer. If an object is located within the specified range (within the green circle), an alert will be triggered and predefined action taken.

Flowchart of perimeter scan proc

Everything is customizable: the layers which can be monitored, the location and range of perimeters, and the actions which can be triggered.

2 - Creating a Perimeter

New perimeters can be created using the Perimeter tool from the Map Tab of the toolbar. Click the Perimeter tool button, and then move the mouse cursor to the center of the area you wish to monitor.

Next, left-click and drag the mouse cursor away from the centerpoint. As you do so, a green circle will appear and a measurement line indicating the approximate radius of the perimeter.

When you have achieved the desired size, release the left mouse button.

3 - Perimeter Settings Dialog

When a new perimeter is created, a Settings Dialog will appear. After completing the fields in this dialog, your Perimeter will be established and ready to scan.

3.1 - Setup Tab

The Setup Tab contains options for selecting which layer or layers you want to monitor, and configuring the alert conditions for each layer.

Name

Enter the name you want to assign to this Perimeter. You can name the Perimeter anything, but each Perimeter must have a unique name. The Perimeter's name will be passed along with other information when an alert is triggered.

Layers to Monitor Panel

In the Layers Listing, you will find every layer which may be monitored by your Perimeter. Note that not all layer types are compatible with Alert Perimeters, so you will not see the entire listing of layers from your map here. Only layers which meed the following criteria are listed:

Layer is dynamic (updates from the Internet)

Layer is vector-based (consists of shapes, lines, or points, but not raster images)

Alerting is permitted (certain layers, such as Lightning Hobbyist are restricted from alerting)

Layers Listing on Setup Tab

Select at least one layer from the listing by checking the box next to its name. After you check the box, you should see the layer appear in the Conditions panel below.

There is no limit to the number of layers you can monitor at the same time. But because you may take only a single action for each Perimeter, you may want to create multiple Perimeters if you want to take different actions for different weather threats.

Conditions Panel

Conditions are the 'thresholds' at which an alert should be triggered.

Conditions Panel on Setup Tab

You probably don't want to sound an alert every time there is a Radar return inside your Perimeter, because many Radar returns are just ground clutter. You want to alert when Radar is indicating severe weather, or at least steady rain. For that reason, you would set the condition to a specific threshold.

To do this, select the desired layer:field from the drop-down list in the conditions panel, then select an evaluator (<, >, =, etc), and finally enter a number into the field on the right.

The above example of Radar > 25 dBZ would look like this:

What do all those list values mean?

Depending on how many layers you have checked off in the Layer Listing, you might see a dozen or more [LayerName:FieldName] options in the conditions drop-down listing:

What do all these options mean?

Here's what they mean. In Weather Defender, each Layer may have multiple fields of information associated with each object in the layer. For example, the Warning Polygons layer contains fields for the type of warning, time issued, time expires, which weather office issued it, and others. Any combination of fields may be used as alert conditions. But most of the time you will only be concerned with one field.

This flexibility in the alert conditions allows you, the end-user, to integrate external 3rd-party data with Perimeter Alerts feature.

Alerting on Any Object

To alert on any object from a particular layer within your Perimeter, regardless of value, select the Layer:* (any object) option from the drop-down list.

This setting is useful for layers in which all objects are considered threats, such as Watch Outlines or Storm Reports.

Configuring Multiple Conditions

Use the conjunction drop down (And/Or) to add more than one condition. For example, if you wanted to alert on Snow, you might set the following conditions:

Rain > 25 dBZ AND Temperature <= 32

You may set conditions on multiple fields from the same layer or across many fields from multiple layers.